The present invention relates to solid propellants and to ballistic additives for use therewith. More particularly, this invention concerns itself with the use of copper salts as burning rate modifiers for solid rocket propellant compositions.
The increased interest and reliance on solid propellant compositions, because of their relatively long shelf life and ease of handling, has created a considerable research effort in an attempt to develop additives which can materially improve the ballistic properties of solid propellant compositions.
One of the primary factors contributing to the ballistic characteristics of solid propellants is the burning rate of the propellant grains. The grains burn in parallel layers. That is, the burning takes place in a direction perpendicular to the surface of the grain and the rate or speed with which the grains burn is referred to as the burning rate. It has the dimensions of velocity and is one of the most important factors to be considered in designing solid propellant rocket motors.
The burning rate of solid propellants is influenced by a number of factors including the pressure of the gas in contact with the burning surface. The rate increases with pressure creating problems with rocket motors requiring a rather constant burning rate with changing chamber pressure. Therefore, the development of additive materials capable of creating desirable ballistic properties, such as burn rate enhancement with concommitant pressure exponent reduction, becomes a very desirable research objective. In furthering this desirable research objective, it was found that the addition of minor amounts of certain copper salts, increased the burning rate of solid propellant grains together with a significant decrease in the pressure exponent. Heretofore, attempts at increasing the burning rate has increased the pressure exponent, thereby severely limiting the application of the solid propellant and the burning rate additive used to alter its burning rate.